generate JIT argument type information for methods

[froydnj]

This enhances CodegenRust.py to output JSTypedMethodJitInfo structures where appropriate. This brings a notable speedup to tests like Dromaeo's dom-attr/getAttribute, which improves by several orders of magnitude with these patches applied.

If there are tricks for addressing the XXX comments, I would appreciate hearing them.

I think this addresses all of #6904.

[frewsxcv]

In case you missed it there are merge conflicts.

[Ms2ger]

Maybe ArgType should use bitflags?

[froydnj]

r? @jdm

[jdm]

-S-awaiting-review +S-needs-code-changes
Ideally we could make ArgType use bitflags (although I don't know if those would work in const values right now), but that would require hand-modifying the rust-mozjs bindings right now. I'd rather use our knowledge of the types involved to make this work correctly.

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Reviewed 1 of 1 files at r1, 1 of 1 files at r2.
Review status: all files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

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^{components/script/dom/bindings/codegen/CodegenRust.py, line 3097 [r2] (raw file):}
If we make this i32 instead of ArgType, we can use | willy-nilly if we cast our ArgType values to i32.

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^{components/script/dom/bindings/codegen/CodegenRust.py, line 3104 [r2] (raw file):}
Then this becomes &${argTypes} as *const _ as *const ArgType.

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Comments from the review on Reviewable.io

[jdm]

@bors-servo: r+

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Reviewed 1 of 1 files at r3.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks pending.

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Comments from the review on Reviewable.io

[bors-servo]

📌 Commit 4f649ac has been approved by jdm

[bors-servo]

⌛ Testing commit 4f649ac with merge d1295e9...

[bors-servo]

☀️ Test successful - android, gonk, linux-dev, linux-rel, mac-dev-ref-unit, mac-rel-css, mac-rel-wpt